The present application relates generally to engine start-stop controls that account for route grade and vehicle mass in stopping the engine of a vehicle.
In automotive vehicles with start-stop control of the engine, the transmission type has a strong influence in vehicle behavior as well as required driver actions during vehicle launching and stopping. One particularly differentiating situation is launching and stopping the vehicle on a grade and what occurs on a launch between the time the driver lifts from the brake pedal and engages the driveline. In the case of an automatic transmission (AT), the torque converter will generate a minor amount of wheel torque in the direction of the selected gear. If the transmission is in a forward gear, the vehicle may experience forward movement on a downhill grade and slight backward movement on a steep uphill grade, while experiencing no movement in other situations.
In the case of an automated manual transmission (AMT) or a manual transmission (MT), there will be a finite period of time where the brake may be released but the driver has not yet applied the accelerator (in an AMT) or released the clutch (MT). During this time, the vehicle will be free to roll if on a grade. Drivers learn to compensate for this roll back through actions such as very rapidly activating the pedals so that any unwanted vehicle movement is minor. Alternatively, a driver may employ the parking brake to keep the vehicle stationary, and release the parking brake in synch with applying driveline torque.
The launch of a vehicle from a stopped position on a grade is further complicated in vehicles equipped with start/stop controls where the engine is initially stopped and must be restarted as part of this launch sequence. In these vehicles the same pedal actions that are used to launch the vehicle are also often used to trigger an engine restart. For example, the engine is restarted when the driver commands a restart, either by stepping in the throttle or releasing the brake pedal.
During the engine restart, the desire is the vehicle will remain stationary. While the vehicle remains stationary on a flat surface, this can't be guaranteed on an inclined surface. Two options exist for preventing roll back in vehicle equipped with start-stop controls. First, the vehicle can be equipped with a device which can provide a hill-hold to preventing the vehicle from rolling back. This increases the cost of the vehicle since such a device must be added to the vehicle and maintained. Second, the engine isn't allowed to stop when the vehicle is on a grade and the restart is avoided, reverting to the behavior of a conventional drivetrain with which most drivers are experienced. However, this reduces the fuel economy benefit of the start-stop system of the vehicle. Therefore, there remains a significant need for the apparatuses, methods and systems disclosed herein.